docs: map the 2020 WCF string-handle wall (R1.4 GETHI blocked)

Probed R1.4 GetHistorianInfo (GETHI) live against the local 2020 server.
GETHI returns native error type 4 / code 1 for the exact native request shape
across 5 handle formats (storage GUID, context GUID, uint decimal/X8/0x-hex)
even with Stat.GetV ×2 priming. Its result is discarded (TryRun) in the only
place it's used, so it was never actually verified to return data managed-side.

This confirms a structural boundary on the 2020 WCF surface: ops taking a uint
client handle work (the proven read/browse/metadata/status/event surface);
ops taking a string GUID handle (ExeC, QTB, QTG, GETHI, GetTepByNm, ...) are
blocked behind an unmapped native session/filter registration. Every remaining
M1 *read* item (R1.1/R1.4/R1.5/R1.6) is string-handle -> all gated on that one
RE target. Reachable uint-handle items: R1.7 event filters, R1.8/R1.9 summary
modes.

New: docs/reverse-engineering/wcf-string-handle-wall.md (full dichotomy + table).
Roadmap R1.4/R1.5/R1.6 struck through; reachable items re-pointed.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/reverse-engineering/wcf-string-handle-wall.md

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+# The 2020 WCF string-handle wall (2026-06-20)
+
+Live-probing the local **Historian 2020** (WCF, port 32568) for HCAL roadmap M1
+surfaced a clean structural boundary on what the pure-managed client can call. It
+explains why R1.1/R1.4/R1.5 all fail and identifies the single RE target that
+unblocks the rest of the M1 read surface.
+
+## The dichotomy
+
+Retrieval/Status/History ops split by the **type of their first (handle) parameter**:
+
+| Handle type | Examples | Status on 2020 WCF |
+|---|---|---|
+| **`uint` client handle** (Open2 output) | `StartQuery2`, `GetNextQueryResultBuffer2`, `IsOriginalAllowed`, `GetTagInfosFromName`/`GetTagInfoFromName` (GetTgByNm), `GetSystemParameter`, `StartEventQuery`, `GetNextEventQueryResultBuffer`, `RegisterTags2`, `EnsureTags2`, `UpdateClientStatus3` | ✅ **work** — the proven read/browse/metadata/status-param/event/write surface |
+| **`string` GUID handle** | `ExecuteSqlCommand` (ExeC), `StartTagQuery` (QTB), `QueryTag` (QTG), `GetHistorianInfo` (GETHI), `GetTagExtendedPropertiesFromName` (GetTepByNm), `GetTagInfosFromName2` (GetTgByNm2), `GetTagidsByTagnameAndSource` | ⛔ **blocked** — native error type 4, code **51 (InvalidParameter)** or **1 (Failure)** |
+
+## Evidence (this probe + prior notes)
+
+- **ExeC** → type 4 / code 51 for every handle variant (storageGuid, contextGuid).
+  Matches `implementation-status.md` ~982 / ~1404 ("StartTagQuery depends on earlier
+  native session/filter registration … do not wire through guessed calls").
+- **GETHI** (`HistorianVersion` param query — the *exact* native request shape from
+  `BuildGetHistorianInfoRequest`, with `Stat.GetV ×2` priming) → type 4 / code **1**
+  for all five handle formats tried: storage-session GUID, context GUID, uint as
+  decimal, uint as `X8` hex, uint as `0x`-hex. In the only place GETHI is used (the
+  event-priming chain) its result is wrapped in `TryRun` and **discarded**, so there
+  was never evidence it actually returns data from the managed client.
+- **GetTepByNm / QTB / QTG / GetTgByNm2** all take a `string handle` → same family.
+
+## Why
+
+The string-handle ops are keyed off a **native-side session/filter registration**
+that the C++ client performs but the managed replay does not reproduce. The uint
+client handle is the Open2 session token the server already trusts; the string GUID
+handle indexes a *different* per-service registration table that stays empty unless
+the native priming is replicated faithfully. `Stat.GetV ×2` alone is insufficient.
+
+## Consequence for the roadmap
+
+Every remaining **M1 read** item is a string-handle op:
+
+- R1.1 `ExecuteSqlCommandAsync` (ExeC) — blocked
+- R1.4 `GetHistorianInfoAsync` (GETHI) — blocked
+- R1.5 extended-property read (GetTepByNm) — blocked (string handle, confirmed)
+- R1.6 localized-property read — same family
+
+So **M1 read-surface completion on 2020 WCF is gated entirely behind one RE target:
+the native session/filter registration for string-handle ops.** Reverse-engineer it
+once and the whole family unlocks. Until then, the alternatives are:
+
+1. **RE the registration** — instrument the native `CRetrievalConnectionWCF` /
+   `CStatusConnectionWCF` priming between Open2 and the first successful string-handle
+   call (capture-tier; the highest-leverage single RE task for M1).
+2. **2023 R2 gRPC server** — these ops are first-class on the gRPC front door, where
+   the handle/envelope differs and the registration wall may not apply.
+
+Do **not** ship any string-handle op via guessed calls (project discipline:
+"leave them throwing until evidence supports an implementation").